Engine synchronizer



Much 29, 1949.

K. L. CURTIS ETAL ENGINE SYNCHRONIZER 6 .Sheets-Sheet l Filed Oct. 4,1943 gmc/M2016 T H :xu ImldmH $00 IPS @n mu .LN L A H E nw TN RN MEA N VL .7 K LA .YN WM mn, S

Mardi 29, 1949 K. L. CURTIS E1' AL 2,465,358

l ENGINE sYNcHRoNIzER Filed Oct. 4, 1943 6 Sheets-Sheet 3 xEu "ETH L. cunn s LA VERNE n. PmLroTT ALLAN e. TnoplPsou March 29, 1949. K, iT,CUR-ns ET AL 2,465,358

ENGINE SYNCHRONIZER Filed oct. 4, 1945 e sheets-sheet 4 o` Q gwua/wtowKENNETH L.CURT|S LA VERNE R.PH|LPOTT ALLAN .G-THONPSON 4, /zfwfm March29, 1949. K. L. cuR'rls 'rAL 2,465,358

j ENGINE SYNGHRONIZER Filed Oct. 4, 1943 v 6 Sheets-Sheet 5 KENNETH LGURTIS LA VERNE `FLPI'IILPOTI ALLAN 6. THOMPSON March 29, 1949. K, L,CURTIS Er AL 2,465,358

ENGINE sYNcHRoNIzER Filed Oct. 1943 SSheets-Sheet 6 gvwam/tow KENNETH L.CURTIS LA VERNE R.PH|LPOTT ALLAN 6. THOMPSON tion taken on the line I-Iof Fig. 2.

Patented Mar. 29, 19.49

ENGINE SYNCHRONIZER Kenneth L. Curtis, United States Navy, La Verne R.Philpott, and Allan G. Thompson, Washington, 1). C.

Application October 4, 1943, Serial No. 504,880

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) The present invention relates in general to synchronizingapparatus for multiple engine power plants and particularly the powerplants of multi-engine airplanes.

An important object is the provision of an ap paratus of minimum weightand bulk having simplicity and ruggedness of structure, andsubstantially shock proof.

Another object is the provision of a simplified control circuit with aminimum number of circuit breaking elements and other electricalcomponents affording improved reliability in operation, low cost upkeepand low power consumption, the latter resulting in reduction of batteryweight and volume.

A further object is the provision of an improved means for effecting astep-by-step adjustment of the speed control means known as notching vwith improvement in operation whereby the adjustment will beeifectedthrough cor rol impulses of substantially constant frequency butwith shorter and shorter impulses as synchronism is approached. j

A further object is the provision of a synchronizing system inwhich thevarious. control circuits and apparatus elements except those requiringdirect mechanical connection with the engines to be synchronized areconstructed and arranged to be mounted as a unit directly on the pilot'sinstrument panel of an airplane.k

A further object is the provision of control elements balanced againstdisplacement by sudden changes in velocity or direction of movement ofthe craft in which the apparatus is carried.

Various other objects and advantages of the invention will becomeapparent from a perusal of the following specification and the drawingsaccompanying the same.

In the drawings:

Fig. 1 is a vertical. longitudinal staggered secyFig. 2 is a vertical,transverse section taken on the line 2-2 of Fig. 1. A

Fig. 3 is a fragmentary detailed View of the selecting and selectablecontact assemblage. Fig. 4 is a fragmentary detail, cross secticnalview'of the velocity fluctuatingmechanism taken on the line l-I of Fig.2.

Fig. 5 is a diagram of a synchronizing system embodying the apparatusshown inFigs. 1 to 4.

Fig. 17, is a diagram of a modication in which both components of therelative movement between the selecting vand selectable contacts areimparted to the selecting contact.

Fig. 8 is a diagram of a modification in which the notching component ofthe relative movement between the contacts is derived from the mastermotor. l

Referring rst to Figs. 1-to 4. these illustrate the mechanical structureof a preferred form of automatic synchronizing device embodying theprinciples of the present invention and capable of being mounted on thepilots instrument panel of an airplane. Here a master motor Iladjustable to a desired standardizing speed, andan enginecontrolledsynchronous motor I0, jointly act upon a speed-comparingdevice -comprising a com pletely rotatable selecting contactI2 and apair of completely rotatabley selectable contacts I3 and I 4 rotatablein trailing and leading relation respectively, with the selectingcontact, the selecting contact I2 being driven by the synchronous motorunit III while the selectable contacts I3 and I4 are driven from themaster motor through transmission gear assemblage I5 to 2li. The termcompletely rotatable as used above, is intended to indicate the qualityof being able to make one or more complete rotations in the manner of awheel as distinguished from a pendulum. Through this connection,disregarding for the moment a velocity fluctuating mechanismincorporated in the gear assemblage I5 to 20 and to be later described,

-the relative motion between the selector contact Vrelative rotation oftheir respective driving Fig. 6 is a diagram of a modification utilizinga v mechanical differential gear for controlling the selection ofdirection of adjustment and an oscillatory movement ofthe selectablecontacts for notching.

motors,` the selecting contact I2 is connected with the driving shaft 2lof the synchronous motor by means of a face plate 22 rotatably mountedon a reduced portion 23 of the shaft and in frictional engagement with afriction slip-clutch element 24 driven by the shaft, the clutch element24 being mounted for rotation with the shaft but slidabe thereon andspring-pressed against the back of the face plate 22 by a compressionspring 25 tensioned to permit the contacts to engage under pressuresuiiicient to effect adequate electrical contact without detrimentalvariation in load on the motors. Insulated control-circuit conductors 26and 21 lead from the selectable contacts I3 and i I4 ring d concentriccontact stud 30 from which electrical connection is extended throughbrushes 3I and 32 to control circuit terminals 33 and 34, respectively.'I'hus with the selecting contact I2 electrically connected with oneside of a source t :gh the hollow drive shaft 28 to a slip ttl..

of current in suitable manner as through the face y plate 22, shaft 2|and frame elements 35 and 38. engagement of the selecting contact withone or the otherof the selectable contacts will extend the connectionthrough one or the other of the terminals 33 or 34 to'differentresponsive means suitably connected to the other side of the currentsource and operable to effect an increase or decrease in the enginespeed through a suitable propellerV pitch-control motor not shown. allin a manner to be later described in reference to the 'circuit diagramof Fig. 5.

between the master motor II and the selectable l contacts I3-II. Thiscomprises 'a countershaft 31 (li'ig` 4) driven from the master motorthrough the gear I1 keyed to the countershai't and meshing with the gearI5 (Fig. 1) keyed to the shaft extension l1 of the master motor. A cam39 (Pigs. 2 and-4) is keyed -on the countershaft 31 between two freegears I3 and I 8, the gear I8 being driven at a speed different fromthat of the gear I1 by the master motor through gear I8 keyed to themotor shaft extension 41, while the gear I8 is driven from the gear I8through an oscillating lever 48 pivotally mounted on the gear i8 at 4Iand engaging the gear I8 through a forked end I2 and a pin 43 carried bythe gear the countershaft 31.

In the present embodiment, the gears are so proportioned that with themaster motor' and gears Il and I8 running at 1800 R. P. M., as where itis desired to maintain an engine at such speed, the gear I8 whichcarries the lever 40 with it around the countershaft will run at 900 R.P. M., while the countershaft 31 driven by gear I1, will run at 960 R.P. M., rotating cam 39 at the latter speed. From the above it will beclear how the lever and cam rotating about the axis of the countershaftin the same direction but at different` angular velocities, will producea rotation of the cam relative to the lever with the result that thelever will be moved through 60 complete cycles of oscillation relativeto the gear I8 duringA each 900 rotations of the gear I8 causing thegear I8 to rotate 'at a fluctuating velocity of 900 R. P. M.

plus or minus the angular displacements betweenI Il and I8. Accordingly,the gear I8 is rotated at a iluctuating velocity averaging the velocityof the gear I8 over successive recurring periods of revolutions of thegear i8. It will be understood that the average velocity of the gear I8need not be equal to that of the gear I8 so long as the ratio of suchaverage velocity to that of the gear I 8 is constant, and thetransmission ratio between master motor II and selectable contactsI3-I4, and between the engine and the selecting contact I2 is such thatthe two sets of contacts will rotate at the same angular velocity whenthe engine is running at a speed predetermined relative to the mastermotor. This fluctuating velooity is transmitted to the driving shaft 28of the selectable contacts through the gear 20. the latter gear beingsecured to the shaft 28 and of equal pitch diameter with the gear I8,the fluctuations occurring at a frequency of 60 per minute. There isthus superimposed upon the basic rotary movement of the selectablecontacts I3and Il a periodic velocity variation resulting in a periodiooscillatory relative motion between the driving shaft 2| of theselecting contact and the driving shaft 28 of the selectable contacts.The amplitude of such oscillatory movement is determined bythe throw ofthe lever lll and is considerably less than the limit of angularmovement of the selecting contact in moving from one to the other of theselectable contacts as determined by the spacing of the latter, with theresult that with both the synchronous motor shaft 2l and theselectable-contact driving shaft 2l running in synchronism and in thesame direction, it is possible for the selecting contact I2 to remainout of engagement with both of the selectable contacts I3 and Il with asubstantial gap on each side. When the synchronous motor element I0slightly gains or loses speed with respect to the master motor. theselecting contact, will engage one or the other of the selectablecontacts with the selectable contact thus engaged. repeatedly moving outoi' and back into engagement with the selecting contact due to theiluctuating velocity of the selectable contact. This results inintermittent brief closures of the control circuit of the pitch controlmotor and a notching operation of the latter. At a greater gain or lossof the synchronous motor with reference to the lmaster motor the rate ofmovement of the selectingicontact toward one or the other of theselectable contacts will be greater so that the intermittent engagementswill occur` sooner and separations later with consequent longerintermittent closures of the control circuit. At still greaterdepartures from synchronism resulting in a rate of relative rotationbetween the synchronous motor shaft and the selectable contactssufilciently great or greater than that necessary to maintain theselector contact in continuous engagement with one of the selectablecontacts, notwithstanding the iluctuating velocity of the latter, therewill result a continuous closure of the control circuit with full andcontinuous operation of the pitch control motor to effect acorrectionfor the'same speed and the selecting contact out of engagement with bothselectable contacts.

`Thus the one set of complementary contacts, the selecting andselectable contacts, perform the two functions of first, the -selectionof one or the other of the two control circuits in response to adeparture from synchronism in one or the other direction and second. theproduction of intermittent brief adjustments or notching during slightdeparture, with continuous vadjustment during wide departure. It is tobe noted here that the notching action is not of that type whichconsists of intermittent brief circuit closures of substantially uniformduration increasing in fre quency with increase in departure until thecircuit closure becomes continuous or continuous in its eiiect 'upon thepitch control motor, but consists oi'lbrief closures of substantiallyconstant frequency of occurrence and of variable duration the periods ofduration overlapping during wide departure from synchronism to producecontinuous correction, and decreasing to a minimum as synchronism isapproached.

It will be clear that this frequency of occur- I rence is determined bythe frequency of the periodic velocity-fluctuation, as determined by thedifference between the angular velocities of the cam 85 driven bv gearI1 and the lever 45 driven by gear I8. while the duration of theintermittent circuit closures for a given machine will vary with'thedifference in speed of the contact-driving shafts 2| and 28.

The speed of the master motor is maintained substantially constant bv agovernor mechanism comprising a hollow, cylindrical governor-weight 45constituting part of a hollow shaft extension 41 ofthe master rcofor andcarrying a surroundving governor weight 48 mounted on the support by arock-shaft 49 extending through the hollow portion of the support inpivotal relation with the latter and fixed to the governor weight. Alever element 55 fixed on the governor rock-shaft bears at its upper end5| against the end portion 52 of a push-rod 53 extending through thehollow shaft 41 into engagement with the switch lever 54 of a vacuumswitch element 55 through a thrust bearing 55 carried in the lever head51. For counterbalancing the weight of elements be'- low the pivot point|55 of the switch lever, such as the lever head 51 and' push-rod 55,there is provided a rectangular frame counterweight |51, surrounding andspaced from the vacuum switch and mounted above the pivot point on apair of arms |55, one of which is shown in Fig. 1, pivoted to the switchholder 255 at 255 coaxially with the switch-arm pivot |55 and connectedbelow the pivot point to the lever head 51. This renders the governormechanism and switch substantially unaffected by sudden changes in foreand aft movement of the ship. The lever head push-rod 55 and governorweight 48 are biased in the retracted vposition shown in Fig. l by acalibrating compression spring 58 arranged to have its degree ofcompression against the lever-head adiustedby a movable abutment element59 adinstable toward and away from the lever-head by a summationscrew-gear 5,0. This screw gear is similar in general arrangement to adifferential screw-gear but differs therefrom in that the two threadedportions 5| and 52 of the screw-bolt 5.8 have yleft and right-handthreads respectively,vso that they actvupon the sliding nut element 54in summation oi their thread pitches, to impart to the abutment element59 a movement of adjustment sumcien't in extent to cover theentiredeslred range of calibration well within a single turn of thespeed control knob 55. In the operation of the calibrating screw-gear.rotation of the control knob and its shaft rotates the screw-bolt 53 bymeans of the splined extension 51 of the latter mounted to slide in andturn with the knobshaft 55 which causes the threaded portion 52 totravel along the stationary nut element 58. The other threaded portion5| being integral or otherwise fixed to the bolt moves with the sameaxial and rotary motion as the threaded portion 52, causing the slidingnut 54, which is mounted to slide without rotation in the sleeve 59, tomove axially in the same direction as the bolt and for a distance ecualtothe axial movement of the bolt plus the relative movement between thesliding nut and bolt due to their threaded engagement. A pointerelement, movable with the knob and knob-shaft, sweeps over a portion ofthe front panel 1|, such panel portion bearing suitable graduations notshown. The switch element 55 may be of any known or other suitable form,preferably of the vacuum type and capable of controlling a speed-controlcircuit for the master motor as indicated in the circuit diagram, Fig.5. Slight, periodically occurring irregularities in load-demand on themaster motor, are in large part absorbed by a fly wheel 200.

A master motor tachometer 12 is mounted on a bracket portion 13 of themain frame element 35. positioned as shown in Fig. 1 to be read from thefront of the instrument panel and having its drive-shaft 14 driven by agear 15 meshing with y the gear I8 on the countershaft 31 and soproportioned with relation to the gears I8 and l5 as to impart to thetachometer shaft 14 a driving speed of one-half the speed of themaster-motor, the tachometer according to general practice giving areading of twice the running speed of its shaft, corresponding toaircraft engine speed, and the actual speed of the master motor in thepresent instance.

A second selectable-contact driving gear 15 (Fig. 2) like the gear 25,is arranged in mesh with the fluctuating velocity gear I9 for drivingthe selectable-contact of a second speed-comparing device not shown,except diagrammatically in Fig. 5, and which, it is to be understood, issimilar in all respects to that constituted by the synchronous motor |0and rotary contact elements l2, I8, and |4 above described, said seconddevice being operatively associated with a second engine to besynchronized with the master motor in a manner similar in all respectsto that described in connection with the first mentioned speed-comparingdevice. Any number of these units may be connected to synchronize asimilar number of controlled devices to the mastermotor.

Referring now to Fig. 5, here is shown diagrammatically the synchronizerof Figs. 1 to 4 with ancillary circuits and apparatus connected forsynchronizing two airplane engines 11 and 18 provided with adjustablepitch propellers 19 and 88 through which adjustment of the engine speed,over a range ample for synchronization, is effected by adjustment of thepropeller pitch. Such adjustment is accomplished through the usualreversible pitch-control motor such as the motor 8|, associated with theengine", having increase and decrease field coils 82 and 88, one foroperating the motor in a direction to increase the propeller pitch andthe other in a direction to decrease the pitch. The field coils 82 and83 are connected for energize-tion over conductors 85 and 88 throughcontacts of relays 81 and 86 controlled from the synchronizing deviceover control circuits 89 and 88 respectively, Each engine is alsoprovided with a tachometertype alternator unit, such as the unit 90associated with the engine 11 for driving its associated synchronousmotor-unit l in the synchronizing device at constant ratio to the speedoi' the engine. Similarly a pitch-control motor 8| and alternator unit92 are operatively connected with the synchronizer device throughsynchronous motor 98, relays 88 and 88 and control circuits 96 and 91. Agang switch 88 is provided for switching the propeller pitch-controlmotors from automatic control by the synchronizing device to manualcontrol, at the same time disconnecting the ships battery 98 from themaster motor il and other elements of the synchronizing device, andopening two phases ot each of the three-phase circuits |00 and |0| whichconnect the engine alternators with their respective synchronous motors.Each of the selector contacts of the different comparing units of thesynchronizer, for example the selector contact I2 of the unit beingdescribed, is maintained in electrical connection with one side of theships battery 98 here shown as the negative side, through a common orground connectionv including the metal frame 38 of the machine, whilethe selectable contacts i8 and I8 connect through the insulated brushes8| and 82 to control circuit conductors 88 and 88 respectively each toone terminal of the relays being connected to the positive side of thebattery by way of battery conductorl |02. The master motor controlswitch 55 is normally biased in the closed position as indicated at theleft of Fig. 5, in which position it maintains a short-circuiting, shuntconnection ID3-|04, around a resistance |05 arranged to be included inseries in the energizing circuit of the master-motor upon opening of theshunt at the switch 55. A condenser |06 in series with a low resistancepilot lamp |01 is connected in shunt of the motor control resistance |01and consequently in'shunt of the control switch 55 as an arc suppressionfilter and indicator, the lamp remaining lighted during rapid closingand opening of the switch.

Operation-In operation, assuming that the gang switch 98 has just beenthrown into the position indicated in Fig. 5 with the Various otherelements in the positions indicated, and the engines 11 and 18 runningsubstantially in synchronism, the three-phase circuits |00 and I0|betweenl the engine alternators 90 and 92 and their respectivesynchronous motor elements l0 and 93 will be completed for operation ofthe motors at constant ratio to the speed oi' their associated engines;the reversing neld coils of the pitch-control motors 8| and 8| will beconnected for control through the contacts of their associated pairs ofrelays 88-81 and 94-88 respectively; andthe positive or ungrounded sideof the ships battery 99 will be connected over battery conductor |02 tothe master motor 4||.- The master motor is now operated under full powersupply over a circuit which may be traced i from battery 98, throughconductor |02, master motor li, switch 58 and back-over ground tobattery 88. The motor speeding up to the predetermined speed to whichthe governor is set maintains a repeated opening and closing of theswitch 55 in response to slight increase and decrease in` speed withreference to the chosen standard. Each opening of the switch uponincreased speed opens the shunt circuit |'88|88 to include theresistance |88 in series in the motor circuit which eilects a reductionin motor speed to :lust below the standard with consequent reclosing ofthe switch and reacceleration of the motor. Thus the master motor ismaintained at a substantially constant speed, the variations in speedbeing so small in degree and their duration so brief as to benegligible. The iluctuating velocity wheel I8 is thus driven at asubstantially constant average velocity of onehalf the motor speed onwhich are superimposed the iiuctuations as above described. Thisiluctuating velocity is imparted to the selectable contacts, of thediiIerent comparing devices through their respective driving wheels 28and 18, to rotate such contacts in the same direction as the selectingcontact but at a fluctuating velocity.

With one ot the engines, for example the engine 11,y rotating offsynchronism say slightlyd faster than the master-motor, theselectingcontact I2, running at slightly higher 'velocity than theaverage speed of the selectable contacts will overtake the leadingselectable contact I8 to engage the latter during the low-velocityperiod of the fluctuating velocity. This connects ground to the controlcircuit conductor 88 to energize relay 81 over 'a circuit which may betraced from ground over selecting contact l2, contact Il, conductor 21,brush 82, conductor 89. relay 81 and back over battery wire |82 throughbattery to ground. Relay 81 becoming venergized closes its contact |88which eilects operation oi' the pitch-control motor 8| with theincrease-pitch field winding 82 over a circuit which may be traced fromground through motor 8|, winding 82, contact |08 of change-over switch88, conductor 88, contact |08 of relay 81, and back over battery wire|02 through battery to ground. Motor 8| now operating under iieidwinding 82 rotates in a. direction to increase the pitch of propeller 19a small amount proportional to the length of time of closure of relaycontact |08 which in turn depends upon the duration of engagementbetween selecting and selectable contacts |2 and I8 except where suchengagement is of shorter duration than the energizing period of therelays which latter period determines the minimum adjustment. The relaysmay be of any known or other suitable type quick to operate and slow torelease, the releasing period chosen being one suicient to permit aminimum effective adjustment of the propeller pitch. As the leadingcontact I8 increases in speed under its fluctuating velocity, it willleave the selecting contact i2.

, Should the pitch adjustment be insumcient to bring the engine speeddown to synchronism,

shaft 2| continuing to gain on shaft 28 will continue to eil'ect a briefengagement between oontacts |2 and I8 at each uctuation in velocitycontinuing the notching operation until synchronism is reached, theadjusting impulses becoming shorter and shorter as synchronism isapproehed, and until the last short impulse resulta in an adjustment ofspeed to very slightly below that of the master motor, whereupon thecontact I2 remains out ot contact with I8, slowly drifting toward I8.With the engine thus in close approximation to synchronism and runningslower than the master motor by an extremely small diil'erence in speed.the selecting contact will remain between andout o! contact with theselectable contacts I I-Il, gradually approaching the decrease-pitchselectable contact I8 as momen the propeller continues at its slightlydecreased speed or decreases further to a speed slightly lower than thatof the master motor, whereupon notching will again take place undercontrol by contacts I2 and |3, through relay 86 and decrease-pitch fieldwinding 83. The control circuit through contacts |2|3 may be traced fromground through contact I2, contact I3, conductor 26 conductor 88, relay86 and back over battery wire |02 through battery to ground. The circuitof pitch-decrease field winding 83 may be traced from ground throughmotor 8|, winding 83, contact I of gang switch 98, conductor 84, contactand back over battery wire |02 through battery to ground.

-Whenever the departure from synchronism is great, the resulting widedifference inl velocity between shafts 2I-and 28 will cause theselecting contact I2 to rapidly overtake the leading contact |4 or beovertaken by the trailing contact I3, as the case may be, maintenance ofengagement without undue transmission of force from one shaft to theother being permitted by the slip in the friction clutch connectionbetween the selecting contact I2 and its driving shaft 2|. Thus duringwide departure the adjustment is continuous with consequent rapidapproach to that nearness to synchronism where notching begins, thenotching continuing with impulses -of substantially constant frequencybut decreasing in duration as synchronism is approached. It willbeunderstood that the engine 18 will be maintained ln synchronism withthe master motor independently of the engine 11 in a manner similar inall respects to that described above for the engine 11. It will also beunderstood that one of the engines through its synchronous motor may beused as a master motor in place of the master motor I|, for driving thegears |5-|6, in which case one of the comparing elements and itsaccessories would be eliminated. For example the-synchronous motor 93 ofthe engine 18 may be used to drive the gears IEB-I6 eliminating themaster motor II and its accesf sories together with the gear 16 andcomparing device and control circuit operated from the latter.

Fig. 6 illustrates diagrammatically a modification in which thecomparing devices, each controlled jointly by the master motor and oneof the engines to be synchronized, for example the engine ||3, comprisesa differential gear 4 having input shafts ||5`and ||6 drivenrespectively by the master motor ||1 and the synchronous motor I|8 ofthe engine |I3, and an output shaft I i9 forl moving the selectingcontact in oneor the other direction according to whichL input shaft isrunning at the higher speed, the output shaft rotating at a speedproportional to the gdegree of departure from synchronism of the twoinput shafts.

For the sake of simplicity and closeness of comparison with the systemfirst described, the differential gearing is shown as having an outputgear I2I of one-half the diameter of the floating gear I22 giving theselecting contact |20 an angular movement equal to the relative movementbetween the two input shafts of the differential. Thus as in the systemrst described, the basic or fundamental relative movement between theselecting contact |20 and the selectable contacts |23 and |24 is equalto the relative movement between the driving shafts IIS-I I6 of thecomparing devices. In the present modification tween the selectingcontact |20 and the selectable contacts |23|24 is achieved by providingVa reciprocating holder |25 for the latter contacts arranged to bereclprocated in any known or other suitable manner as by the link member|28 and eccentric |21 driven from the master motor ||1 through gears I28, |30 and worm gear I3I. The gear ratios are chosen to reciprocate theselectable contacts at the notching frequency desired, for example inthe neighborhood of fifteen cycles per second, although it is to beunderstood that the frequency chosen may vary within wide limits. As inthe system first described, the arrangement is such that the drivingshafts ||6||5 for the comparing device are run at half the speeds of theengine ||3 and master motor, respectively. However in the presentmodification the connections are such that the shafts I6 and ||5 rotatein opposite directions so that the output shaft ||8 will rotate in oneor the other direction according to whether the shaft I|6 is runningfaster or slower than the shaft I|5, the speed of the output shaft beingproportional to the difference between the speeds of these two shafts,in the present case equal to such difference. It is to be understoodthat this ratio is not critical but may vary according to the speed atwhich it is desired to have the selecting contact move in response to agiven degree of departure from synchronism.

As in the system of Figs. 1-to 5, the selectable contacts |23 and |24are positioned inthe path of movement of the selecting contact |20 forabutting engagement therewith, continued movement of the driving shaft||9 after engagement of the contacts being permitted by a suitablefriction slip-clutch connection |32 between the selecting contact andthe shaft. The selecting contact |20 is grounded as indicated at |33 sothat upon engagement with' one or the other selectable contact |23-I24it will complete a circuit from ground through such contact over theconductor |34 or-|35, relay |36 or |31, battery wire |38 and sh'ipsbattery |39 back to ground.

Relays |36 and |31 may be of any known or other suitable type quick tooperate and slow to release. and are arranged, upon energization, toclose their respective contacts |40 and |4| for completion of theenergizing circuits of the decrease and increase iield coilsrespectively, in circuit with the armature of the pitch-control motor|43. The circuit for the decrease coil |44 may be traced from ground atthe pitch-control motor |43 through conductor |45, contact |40, batterywire |38, and battery |39 to ground. Similarly the circuit of theincrease coil |46 may be traced through conductor |41 and contact |4|.

From the above it will be clear that the operation of the' modificationof Fig. 6 is similar in all respects to that of Figs. 1 to 5, notchingtaking place whenever the departure from synchronism is insuicient todrive the selecting contact |28 at a speed to maintain it in engagementwith one vof the selectable contacts regardless of the reciprocatingmovement of the latter, and continuous correction taking place during adeparture sumcient to maintain continuous contact. Here, too, thefrequency of the notching impulses will be substantially constant asdetermined by the speed of the master motor and the gearratio betweenthe latter and the eccentric drive for the selectable contact holder,while the duration of such impulses will vary.l becoming shorter andshorter as synchronlsm is approached. f

the fluctuating velocity of relative movement be- 76 The modificationshown -m Fig. 7 is like that of Fig. 6 except that both components ofthe relative movement between the selecting and selectable contacts areimparted to the selecting contact, the selectable contacts beingstationary: Here, referring for example to the portion of the systemassociated with the engine |48, the fundamental or selecting movementrepresenting in direction the direction of departure from synchronismand in velocity the degree of departure is transmitted to the selectingcontact |48 from the output shaft |80 of the differential gear |8|through a friction slip-clutch |82, arm |88, and link |84 which latteris pivoted at |88 and carries at its free end the selecting contact |48.Thus the selecting movement for effecting selection of one or the otherof the selectable contacts |88 or |80 by the selecting contact |48, isimparted to the contact |48 as an oscillation about the 'pivot |88. Forsuperimposing upon the selecting movement, the oscillatory or notchingmovement, the pivot |88 of the link armA |84 is arranged as afioatingpivot carried on an arm |8| reciprocated by an eccentric |82driven from the master motor |88 in any known or other suitable manneras through the worm gear |84. It will be clear from anI understanding ofthe above described mechanical relations, that when the velocitycomponent imparted to the selecting contact from the differential outputin the direction of a given selectable contact is greater than thevelocity component away from the latter contact imparted through thereciprocating arm |8|, the selecting contact |48 will remain inengagement with the said given selectable contact, continued movement ofthe differential outputshaft during abutment of the selecting contactagainst the stationary slectable contact being permitted by theslip-clufeh |82. As in the previously described system the gear ratiosare so chosen that this condition obtains during a given relatively widedeparture from synchronism. When the degree of departure is below thegiven wide departure notching occurs, the notching impulses occurring ata substantially constant frequency as determined by the frequency ofreciprocation of the arm |8| and at variable duration becoming shorterand shorter as synchronism is approached, the minimum duration beingdetermined by the time constant of the relay |88 or |88 as the case mayIbe.

'Ihe modification shown in Fig. 8 is similar to that of Fig. I in thatboth velocity components are imparted to the one contact element, forexample the selecting contact |81, and differs only in that theoscillatory or notching component is derived from the master motor |88by l2 and the permanently included adjustable resistance |18 anordsadjustment of the amplitude and frequency of the fluctuating velocityresulting from the hunting by the motor |88.

A hunting operation of the master motor takes place as follows. With theparts in the position shown, closure of the power supply switch |14closes the energizing circuit of`relay |88 from battery |18, throughswitch |14, protecting resistance |18, relay |88, governor contacts|11-i 18 and conductor |18 through ground back to battery. Relay |88,becoming energized, closes a shunt around resistance |10 through frontcontact |1| and locksitself through front contact |80 over a holdingcircuit which may be traced from battery |18 through switch |14,resistance |18, relay |88, .contact |88, conductor |18 and throughground back to battery. Maximum power as determined by the adjustableresistance |18 is supplied to`motor |88 from battery |18, throughresistance |18. motor |88. shunting around resistance |10 throughcontact |1|, conductor |18 and ground back to battery.

The motor starting up will increase its speed. the governor |12 movingthe governor controlled movable contact |18 out of engagement withcontact |11 when a predetermined minimum speed is passed and intoengagement with contact |8| when a predetermined maximum speed islreached. At maximum speed, closure of contacts |18|8| completes a shuntacross the terminals causes contact |18 to disengage contact |8|. and

making the latter hunt or fluctuate in velocity at Y substantially thedesired notching frequency and reached, then opening the shunt andmaintaining such circuit condition as the motor loses speed until thegiven low is again reached. The speed governor |12 is of the type shownin Figs. 1 to 4 having an adjustable caiibrating spring which togetherwith the adjustability of resistance |18 upon a drop in speed to thepredetermined minimum causes contact 18 to again engage contact |11. Thecircuit of the relay being open at both contact |1| and contact |11before engagement of contacts |18|11, the relay will remain de-energizeduntil the motor ldrops to the minimum speed, whereupon closure ofcontacts |18|11 will again effect energization of the relay over theinitial energizing circuit previously traced. This results in a shuntingout of the resistance |10 as above described again supplying the motorwith the predetermined maximum power, after which the cycle of operationis rc- Deated indefinitely.

As the control of each engine by themaster motor is effected in the samemanner, a descrip-4 tion of the control of one will suffice, for examplethat of engine |82. Here, as in the previously described modincationsshown in Figs. 6 and 1, the input shafts |88 and |84 are driven inopposite directions one by the master motor and the other by the engine|82, respectively, resultingin a movement of the output shaft |88 at aspeed proportional to the difference in speed of the input shafts and inone or'the other directions according to which shaft is moving faster.In the present instance it is to be assumed that the directions ofrotation of the input shafts are such that the input shaft |88 willimpart a counter-clockwise component to the output shaft |88, asindicated by the adjacent solid-line arrow.

tending to moveithe selecting contact |81 toward the stationary contact|81, the input shaft |84 13 imparting a clockwise component, asindicated by the adjacent dotted-line` arrow, tending to movethe'contact |61 toward stationary contact Upon a wide departure of theengine speed from the mean speed of the master motor, say an increase togreater than the maximum of the master motor fluctuating velocity, theclockwise component imparted to the output shaft |85 will predominatethroughout the entire cycle of fluctuations in velocity of the mastermotor, resulting in a continuously clockwise rotation of the outputshaft |85. This rotation of the output shaft operates through thefriction slip-clutch |88 to move contact |61 into engagement withcontact |86, such enga-gement being maintained to maintain continuousincrease-pitch adjustment of the propeller of engine |82 until, due toa. resulting decreased engine speed, a reverse motion of the outputshaft |85 takes place. Thus a continuous adjustment is effected duringwide departure in either direction from the standard means for which themaster motor is set.

When the engine speed is well above the mean velocity but less than themaximum of the master Vmotor fluctuating velocity, the maximumcounterclockwise component (derived from the master motor) will be onlyslightly above the clockwise component (derived from the engine) andonly while the master motor is near the upper limit of its fluctuatingvelocity. Therefore, the right hand component will predominate for onlya short time and effect a brief separation of contacts "i1-|86. Also,the engine speed, being above that of the master motor through the wholecycle of fluctuation of the latter except while the latter is very nearthe maximum, the engine speed and consequently the left hand componentwill predominate for 'a long portion of the cycle.

'I'hus when the engine speed is well above the mean velocity but lessthan the maximum master motor velocity there will occur a notchingadjustment of long impulses at the substantially constant frequency offluctuation.

Having shown that with the engine speed above the maximum master motorspeed the propellerpitch adjustment will be continuous, and that withthe engine speed slightly below the maximum motor speed but Well abovethe mean, notching will take place with long impulses, it will be clearthat as the engine speed approaches the mean the notching impulses willbecome shorter and shorter.

From the above Vdescription of the various modlcatlons it will be seenthat an important feature common to all, is that both selection ofdirection of adjustment and control of notching impulses are effected bythe same set of contacts, and that notching takes place with relativelylong impulses at departures which are wide but insulcient in degree torequire more than a long` impulse of adjustment, becoming shorter andshorter as the standard speed is approached.

While certain preferred embodiments of the invention have been hereinshown and described for the sake ofdisclosure, it is to be understoodthat the invention is not limited to such specic embodiments, butcontemplates all such modifications and variants thereof as fall fairlywithin the scope of the appended claim.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

In an engine synchronizing system having a controlled engine `with anelectrically operated means for controlling the speed of the controlledengine, and a pair of control circuits for the speed control means onefor effecting an increase and the other a decrease in speed; a controlcomponent comprising a master motor, a completely rotatable selectorcontact, driving means connectable to the engine for driving theselector contact unidirectionally and solely by the engine, a pair ofcompletely rotatable selectable contacts, a second driving meansconnecting the master motor with the selectable contacts for driving thesame unidirectionally and solely by the master motor in a common pathand about a common axis with the selector contact, said selector contactand one of the selectable contacts being adapted to close one of thecontrol circuits, and said selector contact and the other selectablecontact being adapted to close the other control circuit, said seconddriving means having means for periodically varying the ratio oftransmission of motion from the master motor to the selectable contactswhereby the latter are given a fluctuating velocity of unidirectionalrotation having a constant average determined by the master motor only.

KENNETH L. CURTIS. LA VERNE R. PI-IILPOTT. ALLAN G. THOMPSON.

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